With the recent rapid spread of electronic equipment, electromagnetic interference (hereinafter abbreviated as EMI) has given rise to a problem. Counter measures against EMI include circuit means, such as use of anti-noise parts, wire layout, use of a noise filter, grounding, and soft measures; and shield measures, such as cables, connectors, and cages.
The shield measures include a method of using metals, such as a metallic plate, a metallic foil, a metallic net, a metallic mesh, and a metal-plastic laminate; a method of surface treatment for imparting conductivity by zinc spray coating, conductive paste (paint) coating, gaseous phase plating, and electroless plating; and a method of using easy processing plastics having been rendered electrically conductive.
Besides as shields, conductive pastes (paints) are also useful as, for example, adhesives for circuit formation. Known conductive pastes for these uses include thermosetting resins having dispersed therein various conductive metal powders, e.g., copper/acrylic resin, nickel/acrylic resin, nickel/urethane resin, silver/acrylic resin, silver/epoxy resin, copper/phenol resin, and copper/epoxy resin.
Of these conductive pastes, copper/phenol resin type pastes and copper/epoxy resin type pastes have been mainly employed for particular use in shielding circuit bases. The former type pastes have high conductivity reaching a volume resistivity of 1.times.10.sup.-4 .OMEGA..multidot.cm but are insufficient in moisture resistance and adhesion to a resist. The latter type pastes exhibit satisfactory adhesion, etc. owing to the matrix epoxy resin but mostly have a conductivity in the order of 10.sup.-3 .OMEGA..multidot.cm, though some of them have an initial conductivity of about 5.times.10.sup.-4 .OMEGA..multidot.cm, and thus fail to provide a cured film stably having a high level of conductivity.